This invention relates to a cushion fabricated from thermoplastic staple fibers. The cushion is characterized by being formed from multiple thicknesses of non-woven staple fiber webs, overlaid, compressed, heated and fiber-bonded under compression to form a cushion having different densities in different regions of the cushion.
Cushions of the type constructed according to the invention are intended to have application in chairs, sofas and other residential and commercial furniture products, in vehicle seats, such as automobile and aircraft occupant seats, and other cushion products. The particular embodiment disclosed in this application relates to an automobile seat-bottom cushion such as could be used as a driver or front passenger seat. Seat-back cushions and other cushion elements and components can also be made according to the invention disclosed in this application.
This invention disclosed in this application is, by way of example, fabricated according to a method and apparatus for forming a non-woven batt by means of vacuum, as disclosed in applicant's prior U.S. Pat. Nos. 4,668,562, 4,753,693, and 5,079,074. Batts according to these prior patents are characterized by having a relatively high density which renders them suitable for uses such as mattresses, furniture upholstery and similar applications where substantial density and resistance against compression is desired, together with substantial resilience which will return the batt to its shape and thickness after compression for an indefinite number of cycles.
Cushions according to this invention can also be manufactured by other methods, including the "air lay" method and using a fiber shaker to deposit cross-thicknesses of fibers onto the batt as it is formed.
U.S. Pat. No. 5,079,074 discloses a batt which has a dual density, defined as having two batt layers, one on top of the other, with one of the layers has a greater density than the other. However, the batts are the same thickness at all points, and the density is uniform along any horizontal plane.
There are applications where the density of a seat-bottom or seat-back cushion should optimally be greater at particular places along the surface of the cushion than at other places. For example, in the embodiment of a seat-bottom cushion for an automobile seat disclosed in this application, the left and right sides of the cushion include bolsters which flare upwardly to form supports for the lateral aspect of the hips and thighs of the seat occupant. This is particularly desirable in vehicles, since centrifugal force created by turning tends to project the occupant radially outwardly along a vector which varies according to the tightness and speed of the turn. The center portion of the seat cushion under the buttocks is lower, resulting in a "bucket" in which the occupant can seat without undue sliding, swaying or leaning as the automobile is turned.
Most prior art seats, such as used in automobiles, aircraft and other vehicles are fabricated of polyurethane foam. The seat is molded into a desired shape and size by introducing a predetermined-size charge of polyurethane precursor and catalyst under pressure into a closed mold. The precursor and catalyst react to create a gas which disperses through the mold, expanding the charge in the mold until the mold is completely filled. The polyurethane is cured by, for example, heat, and the mold is opened revealing a bun of polyurethane foam. The density of the bun at this point is essentially equal throughout its width, length and depth, since the gases generated in the mold expand equally in all directions.
For this reason, integrally-formed extensions, flanges, bolsters and the like tend to provide inadequate support. Over time, these areas can fragment or detach from the rest of the seat from wear resulting from, for example, a seat occupant first sitting down onto the edge of the seat as the vehicle is entered before swinging fully onto the seat, and leaning onto the edge of the seat as the vehicle is exited.
This problem can be reduced somewhat by fabricating the seat cushion from separate pieces of foam of differing densities. This is now typically done in higher priced automobile seats and in aircraft seats. This can be done by cutting blocks, strips, wedges and other shapes from separate pieces of foam of differing densities, and assembling the pieces in a jig to form the cushion. The foam pieces are joined by bonding with adhesives.
In the case of an automobile seat-bottom cushion, wedges of high density foam may be bonded to the sides of a less-dense central portion to form side bolsters, or the wedges may be inserted under the edges of the cushion or in pockets in the sides of the cushion to provide greater resistance to deformation caused when entering or exiting the vehicle, or when the occupant leans against the bolsters during turns.
The process of making such a cushion is labor-intensive, subject to numerous manufacturing variables, requires skilled labor, and creates substantial waste as the various shapes are formed from larger blocks of foam. In any event, the joint lines between areas of differing-density foam create potential weakness zones where the cushion is subject to breakage as the seat wears.
The invention described in this application avoids these problems by making multi-density cushions in a continuous process from thermoplastic staple fiber blending through to the formation of a cushion "blank" ready for molding into its final shape. The cushion is then encased within a upholstery dress cover and mounted on a seat frame.
There are a number of advantages to be achieved by construction of cushions from this type of synthetic, staple fiber material. Such fibers are inherently lightweight and therefore easy to ship, store and manipulate during fabrication. These fibers are also generally less moisture absorbent than natural fibers such as cotton, or cellulosic based synthetic fibers such as rayon, and far less subject to fragmenting and deterioration than polyurethane foam.
Therefore, cushions as disclosed in this application and made from these fibers can be maintained in a more hygienic condition. Many such fibers also tend to melt and drip rather than bum. While some of these fibers give off toxic fumes, the escape of such fumes can be avoided or minimized by encapsulating the cushion in a fire retardant or relatively air impermeable casing. This is a particularly important factor in automobiles, aircraft and other vehicles where emergencies involving fire are possible.
The resiliency inherent in synthetic fibers such as nylon and polyester is caused by the plastic memory which is set into the fiber during manufacture. By plastic memory is meant simply the tendency of a fiber to return to a given shape upon release of an externally applied force. Unless the plastic memory is altered by either elevated temperature or stress beyond the tolerance of the fiber, the plastic memory lasts essentially throughout the life of the fiber. This can make formation of a batt by compressing without bonding a much thicker, less dense batt difficult because of the tendency of the fibers to rebound to their original shape. Such fiber batts can be maintained in a compressed state, but this has sometimes involved the encapsulation of the batt in a cover or container. All of these methods create other problems such as unevenness and eventual deterioration of the batt due to fiber shifting, breakage and breakdown of the mechanical structure which maintains the compressed batt.